1. Field of the Invention
The present invention relates to a magnetoelastic wave device, such as a phase shifter, a variable delay circuit, a tuner, an oscillator or a filter, which utilizes bulk elastic waves or surface acoustic waves.
2. Description of the Related Art
Magnetoelastic wave devices utilizing the magneto-striction have been studied. These devices have their input-output characteristics changed to a desired value when a magnetic field is applied to them, thereby changing the speed of sound. Among these devices is the delay element disclosed in IEEE Trans. Mag., MAG-16 (1980), p. 916, which comprises an LiNbO.sub.3 substrate and a TbFe.sub.2 amorphous magnetostrictive alloy layer.
Each magnetoelastic wave device hitherto developed is not practical in two respects. First, the sound speed is changed by only 0.3% at most. Second, the propagation loss of energy (i.e., attenuation) is great.
Another type of a magnetoelastic wave device is disclosed in D. C. Webb, K. L. Davis, N. C. Koon, and A. K. Ganguly, Magnetoelastic Surface Wave Propagation in a Low-anisotropy Rare-earth-iron Compound at 80 MHz, Applied Physics Letters, Vol. 31, No. 4, Aug. 15, 1997, pp 245-247 and also in A. K. Ganguly, K. L. Davis, and D. C. Webb, Magnetoelastic Surface Wave on the (110) Plane of Highly Magnetostrictive Cubic Crystal, J. Appl. Phys., 49(2), February, 1978, pp. 759-767. Magnetoelastic wave devices of this type have not been put to practical use, since they fail to meet two requirements, i.e., (i) a high ratios of sound speed and (ii) small propagation loss.
As described above, the magnetoelastic wave devices hitherto developed, though seeming to have no practical value, can function as a tuner, provided that their input-output characteristics are changed by applying a magnetic field to them. As is known in the art, magnetoelastic wave devices are very small. Hence, it is desired that the magnetoelastic wave device, which functions as a tuner, be invented and incorporated in a system, so that the system may be reduced in size.